function res = trial3(omega,x,h)
res1 = BD_sin(omega,x-h,h);
res2 = BD_sin(omega,x,h);
res3 = BD_sin(omega,x+h,h);
res4 = BD_sin(omega,x+2*h,h);
res = (res4-res3-res2+res1)/(2*h^2);